CA1188119A

CA1188119A - Fluidic cryogenic refrigerator

Info

Publication number: CA1188119A
Application number: CA000420662A
Authority: CA
Inventors: Domenico S. Sarcia
Original assignee: CVI Inc
Current assignee: CVI Inc
Priority date: 1982-04-19
Filing date: 1983-02-01
Publication date: 1985-06-04
Also published as: FR2525331B1; ZA832079B; GB2120371B; US4391103A; GB8303921D0; JPS58190665A; DE3313506C2; FR2525331A1; DE3313506A1; JPH0263148B2; GB2120371A

Abstract

FLUIDIC CRYOGEMIC REFRIGERATOR

Abstract Of The Disclosure The cryogenic refrigerator includes a movable dis-placer within an enclosure having first and secondchambers of variable volume. A refrigerant fluid is circulated in a fluid path between said chambers by movement of the dis-placer. A spool valve controls introduction of high pressure fluid and low pressure fluid. The displacer movement is controlled by fluidic pressure instead of an electric motor.

Description

FLUIDIC CRYOGENIC REFRIG~RATOR

Background _ The present invention is an improvement on the Gifford-21cMahon cycle. Familiarity with said cycle is assumed. Representative prlor art patents teaching such cycle include U.S. Patents ~,966,035r 3,188,~1~. 3,21~,~15;
and 4,305,741.
In certain environments, such as a super conducting ~uantum interEerence device, the magnetic flux of an electric motor cannot be tolerated. Hence, there has been proposed a -fluidic unit to cause movement oE the displacer.
For example, see U.S. Patent 4,310,337. Fluidic reEriger-ators have certain clisadyantages. namely lack of control of the displacers so that a full pressure charge of gas is introduced in each cycle and the ob~ectional noise when the displacer bottoms out at the end o-E each stroke. The present invention solves those problems.
_mmarv Of Th _Invention The present invention is directed to a cryogenic refrigerator in which a movable displacer deEines ~ithin an enclosure Eirst and second chambers of variable volume.
A refrigerant fluid is circulated in a fluid flow path between the Eirst chamber and the second chamber by move-ment of the displacer. Movement of the displacer is con-trolled in part -through the introduction oE hiyh pressure Eluid and the discharge oE low pressure Eluid.

The reEriqerator includes chamber means Eor gul(ling a slide having an axial passage. The .sLide is connect--d to the displacer. ~ piston is connected to the slicle for controlling movement oE the displacer in response to ~3as at an interme~liate pressure actinq on the piston.
The passa~e in the slide has a restriction. ~ valve is provided with a spool valve member for controlling flow oE the high and low pressure Eluid. Means is provided in-cluding a conduit communicating one end o-f the spool valve member with the end of said chamber means remote from said displacer ~Eor introducing high fluid pressure into the conduit to shift the spool valve member when the displacer is at bottom dead center.
It is an object of the present invention ~o provide a fluidic cryogenic refrigerator wherein eEficiency and reliability are improved by controlling movement of the displacer by a fluidic arrangement which acts as a dashpot during a stroke of the displacer and as a shock. absorber at the ends of the stroke.
It is another object oE the present invention to pro-vide a fluidic cryogenic refrigerator which is simple and reliable.
~ ther objects and advantages will appear hereinafter.
For the purpose oE illustrating the invention there is provided in the drawing a form which is presen-t:Ly pre ferred it being understood however, that this invention is not limited to the precisè arrangements and instremen-talities shown.
Figure 1 is a vertical section view of a refrigerator in accordance with a Eirst embodiment oE the prsent inven-tion with the displacer at top dead center position.
Figure 2 is a vie~ similar to Figure 1 but showing the displacer at an intermediate position.
Figure 3 is a view similar to Figure 1 but showing the displacer at hottom dead center.

Detailed Description Referrlng to the drawings in detail, wherein ~ike numerals indicate like elements, there is shown a refriger-ator in accordance wi-th the present in~ention designated generally as 10. As il'Lustrated, the refrigerator 10 has a first stage 12 and may have a second stage. When in use said stages are disposed within a vacuum housing no-t shown.
It is within the scope of the present invention to have one or more of such stages, Each stage includes a housing such as housing 16 within which is provided a displacer 18. A seal 19 is provided on displacer 18 for contact with housing 16. The displacer 18 has a length less than the length of the housing 16 so as to define a warm chamber 20 thereabove and a cold chamber 22 therebelow. The desig-nations warm and cold are relative as is well known to those skilled in the art.
A heat station 24 in the form of a tube having a flanged ring and made from a good heat conductive material is attached to the housing 16 and surrounds the cold chamber 22. Heat station 2~ may have other constructions as is well known to those skilled in the art, Within the displacer 18, there is provided a regen-erator 26 containing a matrix. Ports 28 communicate the upper end of the matrix in regenerator 26 with the warm chamber 20. See Figure 2. Radially disposed ports 30 communicate the lower end of the matrix in regenerator 26 with a clearance space 32 disposed between the outer peri-phery of the lower end of the displacer 18 and the inner periphery of the housing 16. Thus, the lo~er end of the matrix in regenerator 26 communicates with the cold chamber 22 by way of ports 30 and clearance 32.
The matrix of the regenerator 26 is preferably a stack of 250 mesh material having high specific heat such as oxygen free copper. The matrix has low void area and ~ow pressure ~rop. The matrix may be other materials such as lead spheres, nylon, glass, et~.

~ a~

A Slide 46 is connected to the upper end of the displacer 1~. The slide 46 is surrounded by and guic1ed by clearance seal sleeve bearings 47, ~ and 49 attache~ to the housing 3~. Bearings 47, 48 and 49 are preferably made from a ceramic material. Slide 46 has cylindrical bearing inserts 5~ in sliding contact with the inner periphery of the sleeve bearin~3s 47. and 49. An axial flow passage 52 is provided in the slide 46. Slide 46 is longer than the sleeve bearings and has radial ports 55 located above a restriction 54 in the passage 52. When the slide 46 is below top dead center, as shown in Figure 2, the chamber means thereabove and within the bearing 49 is designated 56.
The hol~sing 3~ includes a bore 53 parallel to the slide 46. I~ithin the bore 5~ there is provided a clear-ance seal sleeve bearing 6n preferably made from a ceramic material. Within the sleeve bearing 60, there is provided a reciprocable spool valve member 62 having an axial flow passage 64. It will be noted that the member 62 has a length less than the length of the sleeve hearing 60 so that passage 64 communicates with chamber 65 therebelow.
Ad~acent the upper end of member 62, there is pro-vided a restriction 66 in passage 64. The upper end of the passage 6~ communicate.s with chamber means 56 by way of conduit 67. A groove 68 is provided on the outer periphery of spool valve member 62. In the position of spool valve member 62 as shown in Figures 1 and 2, one end of groove 68 communicates with the warm chamber 20 by way of passage 70.
A high pressure port 74 is provided in housing 3~ and is blocked by the spool valve member 62 in the position there-of as sho~n in Figure 1. As will be made clear herein-ater, port 7~ is adapted to communicate with cha~ber mean~
56 by way of passage 76 when the displacer 1~ i5 at bottom ~ead center.
In the position of the spool valve member 62 as shown in Figure 3, the upper eod of the passage 69 is blocked by member 62. Port 55 of slide 46 communicates with passage 69 and groove 68 when slide 46 ;s at top dead center. See Figure l. Port 82 communicates with the .suction side of a compressor 84~ The output Erom compressor ~4 communicates hy way oE cond~lit 86 with the high pressure port 74.
The housing 38 is constructecl oE a number of com-ponents so as to Eacilitate machininq oE the housing, assembly and access to the spool valve member 62 and slide 46. The manner in which housing 38 is comprised of a plurality of components is not illustrated hut will be obvious to those skilled in the art. The refrigerator lO
is preferably designed for use with a cryogenic fluid such as helium but other fiuids such as air and nitrogen may be used. The refrigerator lO was designed to have a wattage output of at least 65 watts at 77K and a minimum of 5 watts at 20K.
The upper end of slide 46 is smaller in diameter than the lower end. A piston 88 is a-ttached to slide ~6 and is supported by the larger diameter lower portion thereof.
A differentiaL reaction surface 87 is provided on piston 88. Piston 88 is disposed in chamber 90 defined by bear-ing 48. The space 92 above piston 88 is at a minimum when the displacer 18 is at top dead center as shown in Figure l and at a maximum when the displacer 18 is at bottom dead center as shown in Figure 3O The space below the piston 88 is designated 94.
Space 92 is in continual communication with space 94 by way of passages 96, 97, 98. A needle valve lO0 controls flow between passages 96, 97. A needle ~lalve 102 contro:ls flow between passages 97, 98. Passage 96 communicates with space 92 at a location which traps gas between piston ~8 and the upper end oE chamber 90 to act as a shock absorber.
The passage 98 communicates with space 9~ in a similar manner.
The needle valves lOn and 102 are set at the same Elow rate and have a valve member with a smal1 taper such as 2. A pointer is provided on valve memher 100 Eor correlation with ~racluations on pl.ate ln~. A similar pointer is provitle(1 on valvt? rlember 102 for correlation with gradl~ations on plate l~h. mhe needl~ valves 10() 102 control th~? flow oi~ gas betwe~n spaces 92, 94 an~l act as a dashpot. Hence the cycles per min~te may be varied by adjusting each valve by the .same amount.
Passage ~7 co~mu~icat~s with a source of interm~diate pressure such as helium gas at 200 psi hy way of conduit 108 containing valve 110. The specific amount of the interme~iate pressure is relative to the hiyh pressure at the output of compressor 84 which may be 300 psi and the low pressur~ at the input of compressor 84 which may he 100 psi.
Opera ion As shown in Figur~ 1, the displacer l$~ is at top dead center. Spool val~e memher 62 has iust moved to its uppermost position wherein chamber 20 communicates with the suction si~e of compressor û4 by way oE passage 70, groove 58, and port 82. The chamber 65 below spool valve member 62 is also exhausted by way of passage 64, conduit 67, passage 52 and passage 69. High pressure gas is trapped in passage 76.
As the displacer begins to mo~7e downwardly by differ-ential pressure on piston surface 87 due to the compression of the trapped intermediate pressure gas, the cold low pressure gas in chamber 22 moves upwardly through the regenerator 26 and is exhausted. As the low pressure gas moves through the regenerator 26, it absorbs heat from the regenerator thereby cooling the regener-ator. As shown in Figure 2~ the displacer is moving down and toward bottom dead center and port 55 misaligns with passage 69.
When the upper end of slide 46 uncovers passage 76, the displacer 18 will be at bottom dead center as shown in Figure 3. Accuracy in locating the passage 76 directly effects efficiency As passage 76 is uncovered, high pressure gas from port 74 flows from passage 76 to chamber means 56 and conduit 67. Just before passage 76 is uncovered, piston 88 closes off passage 98 and traps gas at the intermediate pressure in space 94 therebelow. ~le trapped gas is com?ressed and ahsor~s the kinetic energy of ~is-plac~r 18 therebv stop~in~ the downward movement. The pressure between restrictors 54 and 6~ increases. When the hi~h pressure qas overcomes the low pressure fluid trapped in chamber 65 member 62 descends from the position shown in Figure 2 to the position shown in Figure 3. Now the entire system except for passage 69 contains high pressure gas. The displacer 18 is at bottom dead center.
The function of the regenerator 25 is to cool the gas passing downwardly therethrough and to heat gas passin~
upwardly therethroughO In passage downwardly through the regenerator, the gas is cooled thereby causing the pressure to ~ecrease and further gas to enter the system to maintain the maximum cycle pressure. The ~ecrease in temperature of the ~as in the chamber 22 is useful refrigeration which is sought to ~e attained by the appartus at heat station 24. As the gas flows upwar~ly through the regenerator 26, it is heated by the matrix to near ambient temperature thereby cooling the matrixO
The slide 46 is moved upwardly from bottom dead cen-ter as shown in Figure 3 with the displacer 18 by Aif-ferential pressure on piston 88 as high pressure gas moves downwardly into chambers 2n, 22 and the void volume of regenerator 2fi. Port 55 communicates with passage 69 when cold volume is at maximum and just before top ~ead center is reached. This immediately places passage 52 and conduit 67 in communication with the low pressure gas in passage 69 and when the spool valve member 62 shifts the suction side of the compressor 84. Piston 88 closes off passage 96 and traps gas at the intermediate pressure in space 92. The trapped gas is compressed and absorbs the kinetic energy of displacer 18 thereby stopping its upward movement.
The hi~h pressure gas trapped in chamber 65 raises the spool valve memher 62 from the position shown in Figure 3 to the position shown in Figure l as the clisplacer 18 reaches top ~ead center. One cycle is now co~pleteO
~ligh press~re gas exhausts u~ through the regenerator 26 I

-a-thereby cooling the matrix. A typical emhodiment operates at the rate of 7~-~0 cycles per minute. The length of the stroke of the movable members is short such as 12mm for valve memher h2 and 30mm for the displacer. Valve member 62 need not have axial flow passage 64 but instead may be a solid spool valve member which responds to differential pressure.
As piston a8 moves down with displacer 18, gas in space 94 flows to space 92 via passages, 98, 97 and 96.
Also, gas from conduit 103 flows into space 92. As the piston ~8 moves up gas from space 92 flows into space 9~ with part of the gas flowing into conduit 108 to the intermediate source. On the downstroke, the pressure on surface ~,7 at tlle interme~iate pressure overcomes the opposing reaction of the low pressure gas. On the up-stroke the high pressure qas overcomes the opposing reac-tion of the intermediate pressure gas on surface ~7. ~he speed of the stroke in either direction will be the same so long as the needle valves 100, 102 are at the same position of adjustment.
The present invention may be embodied in other spe-cific forms without departing from the spirit or essential attrihutes thereof and, accor~ingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicatin~ the scope of the invention.

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Claims

1. In a cryogenic refrigerator in which a movable displacer means defines within an enclosure first and second chambers of variable volume, and in which a refrigerant fluid is circulated in a fluid flow path between said first chamber and said second chamber by the movement of said displacer means controlled in part through the introduction of high-pressure fluid and the discharge of low-pressure fluid, chamber means for guiding a slide connected to the displacer means, said slide having an axial passage communicating with one end of said chamber means remote from the displacer means, a piston coupled to said slide for controlling movement of the displacer means, valve means for metering flow between opposite sides of said piston, the cross-section of said slide being smaller on one side of the piston than on the other side, said passage in said slide having a restriction, a valve having a spool valve member for controlling flow the high and low pressure fluid, means including a conduit communicating one end of said spool valve member with said one end of said chamber means for introducing high fluid pressure into the conduit to shift the spool valve member when the displacer means is at one of the extremities of its move-ment.

2. Apparatus in accordance with claim 1 wherein said valve means including a pair of spaced needle valves, a valved conduit communicating with each needle valve and adapted to communicate with a source of gas at an inter-mediate pressure.

3. Apparatus in accordance with claim 1 wherein said piston is arranged to trap fluid thereabove when the displacer means is at top dead center so that the trapped gas acts as a shock absorber.

4. Apparatus in accordance with claim 1 wherein said piston is arranged to trap fluid therebelow when the displacer means is at bottom dead center so that the trapped gas acts as a shock absorber.

5. Apparatus in accordance with claim 1 wherein said spool valve member has an axial passage containing a restriction therein adjacent the end thereof communi-cating with the conduit.

6. Apparatus in accordance with claim 2 wherein said needle valves are adjusted to the same flow rate.

7. Apparatus in accordance with claim 1 including a discrete ceramic clearance seal sleeve bearing for said slide, piston and spool valve member.

8. Apparatus in accordance with claim 1 including passage means for venting said passage in said slide and said conduit as the displacer means approaches top dead center to thereby enable the spool valve member to reverse its positions with respect to high and low pressure.

9. A cryogenic refrigerator comprising a movable displacer within an enclosure having first and second chambers of variable volume and in which a refrigerant fluid is circulated in a fluid flow path between said first chamber and said second chamber by the movement of said displacer controlled yin part through the introduction of high-pressure fluid, chamber means for guiding a slide connected to the displacer, said slide having an axial passage communicating with one end of said chamber means remote from the displacer and said first chamber, a piston coupled to said slide intermediate its ends for controlling movement of the displacer, means for cycling gas at a metered rate between opposite faces of said piston when said displacer moves, said passage in said slide having a restriction, a valve having a spool valve member for controlling flow the high and low pressure fluid, means including a conduit communicating one end of said spool valve member with said one end of said chamber means for introducing high pressure fluid into the conduit to shift the spool valve member when the displacer is at bottom dead center, said spool valve member having an axial passage containing a restriction therein adjacent the end thereof communicating with the conduit.

10. Apparatus in accordance with claim 9 wherein said means for cycling gas includes first and second valved passages each communicating with one of the spaces on opposite sides of the piston at a Location wherein it is blocked by the piston in a manner whereby gas will be trapped to absorb the kinetic energy of the displacer and stop the displacer at one end of its stroke.